1. Field of the Invention
The present invention relates to an apparatus for applying solid developer particles to the recording element of a non-impact printer.
2. Description of the Prior Art
In present-day data processing equipment, fast printers are finding increasing application, in which the printing of the characters is effected without requiring raised type impacting on a recipient sheet of paper. These printers, called non-impact or strikeless transfer printers, ordinarily comprise a recording element which usually consists of a rotary drum or an endless belt, on the surface of which sensitized areas can be formed by electrostatic or magnetic means. These sensitized areas are also called latent images and correspond to the characters or images to be printed. These images are then developed, that is to say, made visible, with the aid of a powdery developer deposited on the recording element, and which is only attracted by the sensitized areas thereof. Thereupon, this recording element is brought into contact with a sheet of paper so as to permit the developer particles that have been deposited on these areas to be transferred onto this sheet in order to be fixed definitively thereon.
To apply this powdery developer to the recording element of a printer of this type, various applicator means have been used. For example, a device has been employed which comprises a housing containing the powdery developer, said housing having an opening past which moves the recording element. The inking of the recording element is effected by means of a cylindrical brush which, turning within the housing, projects the developer particles onto the surface of the element moving past said opening. This device has not given complete satisfaction due to the fact that it causes the formation of a cloud of developer particles which spreads on the outer surface of the case. Such clouds are particularly disagreeable for persons who are near the printer and who are attached by this cloud. Another problem with such devices is that they cause an undesirable electrification of the particles which, projected onto the recording element, can continue to exist on the areas that have not been sensitized by the recording element as a result of electrostatic attraction.
If the developer is capable of being attracted magnetically, a magnetic roller of the type as described and shown in French patent 1,566,007 and comprising a set of elongated magnetic elements, one arranged beside the other about a shaft parallel thereto, can be utilized to apply this developer. Each of these magnetic elements is magnetized radially so as to exhibit a constant magnetic polarity throughout the length thereof. The magnetic polarities exhibited by two adjacent magnetic elements have opposite signs. This magnetic roller, which has given good results when used in an apparatus for developing latent images with electrostatic charge for transporting a powdery developer which is capable of being attracted magnetically, has not been completely satisfactory when used as a roller for conveying a powdery developer in an apparatus for developing magnetic latent images such as, for example, a magnetic printer. Indeed, due to the fact that this magnetic roller is placed in the immediate vicinity of the element for recording latent images, this recording element is necessarily subject to the action of the magnetic fluxes generated by the magnetic elements of this roller. As a result, the information recorded on this recording element runs the risk of being substantially altered at the moment when it moves past this roller for applying the developer.
This latter drawback can be overcome by inserting between the applicator roller and the recording element a deflector intended to collect the developer particles conveyed by the roller. The deflector has one of its edges arranged in the immediate vicinity of the recording element so as to form therewith a trough having substantially the shape of a dihedral, in which the developer particles collected by the deflector will be gathered. Thus, an applicator means is obtained of the type described and shown in French patent No. 2,408,462 and in which the recording element is moved in a direction such that the collected particles in the trough are carried to the angle of the dihedral. The particles carried beyond said angle remain applied only to the sensitized areas of the recording element. However, it has been noted that if the applicator means contains a conveyor roller of the type as described in the aforementioned French patent No. 1,566,007, the developer particles would be aligned along the external magnetic lines of force which, on the surface of the conveyor roller, extend from each one of the magnetic elements with a magnetic north polarity to each one of the neighboring magnetic elements with a magnetic south polarity. Since these external field lines form arches which are oriented perpendicularly to the roller's axis of rotation, the developer particles, placed along these field lines, form chains of particles which are arranged perpendicularly to said axis. Under these circumstances, when these particle chains are stopped during passage by the baffle plate, they break up, but continue to form within the trough, fragments of chains having an orientation which is substantially perpendicular to the surface of the recording element. The result is that these particles, when they are applied to the sensitized areas of this element, have the tendency to enter into combination with one another so as to form thread-like aggregates of particles resulting in the appearance of trains of particles on the surface of the recording element and, thus, in trains that are particularly disagreeable to behold for the characters formed during the transfer of these particles to the paper.